Tobraviruses (Virgaviridae)

Abstract

The genus Tobravirus is comprised of three species, the type species Tobacco rattle virus (TRV) together with Pea early-browning virus (PEBV) and Pepper ringspot virus (PepRSV). The Tobravirus genus is positioned within the Virgaviridae family. Tobraviruses have a genome of two, positive-sense, single-strand RNAs that are packaged separately into rod-shaped particles. The larger genomic RNA (RNA1) is about 7 kb in length and encodes proteins involved in replication and movement of the virus within plants. The smaller RNA (RNA2) varies in length from 1.8 to 4.2 kb and encodes the coat protein and usually two other non-structural proteins involved in virus transmission. In some situations, RNA1 can cause a systemic infection in the absence of RNA2, and without the formation of virus particles. RNA2 of different isolates of TRV varies considerably in sequence and gene organization. The coat protein also varies significantly between isolates giving rise to many different serotypes. The tobraviruses are most closely related, in terms of genome organization and viral protein sequence, to members of the genus Tobamovirus. Tobraviruses are transmitted between plants by root-feeding nematodes of the genera Trichodorus and Paratrichodorus, and in some plant species are also seed transmitted.